This invention relates to a combustion control device using an electrode rod to be put into a flame.
Devices which perform combustion control by detecting the indoor oxygen content which depends on the condition of the flame of burner are conventionally known. One such device is disclosed in Japanese Patent Publication No. 50-28654. In combustion control, an electrode rod is first put into the flame of the burner. If an a.c. voltage is then applied between the electrode rod and the body of the burner, a d.c. current (hereinafter referred to as flame current) is produced between them by the agency of the flame. The flame current changes according to the length of the flame, which varies with the indoor oxygen content. Therefore, combustion control may be performed in accordance with the result of detection of the indoor oxygen content on the basis of the intensity of the flame current. The flame of the burner becomes longer as the indoor oxygen content is lowered. Further, the flame current is reduced as the flame is lengthened. Thus, a decrease in the flame current indicates the degree of reduction of the indoor oxygen content. The flame current of the burner is zero before the burner is ignited. The flame current takes a steady-state value while the burner is operating with a normal indoor oxygen content. If the indoor oxygen content is lowered, then the flame current decreases gradually from the steady-state value.
The flame current depends not only on the change of the indoor oxygen content, but also on the supply voltage supplied to the electrode rod. In other words, for different supply voltages a given flame current corresponds to different indoor oxygen content levels. Therefore, a change of supply voltage causes faulty operation of the combustion control device.